Hari
You've got the main reason. Pro Tools has dedicated hardware based on DSP technology, with dedicated hard disks for recording onto. They've been working with this architecture as long as Cubase, but while Cubase has focused on supporting industry standard sound cards Pro Tools has more or less always used dedicated hardware. In fact their first foray into the budget market was only a couple of years ago with the Digi001.
Pro Tools has it's problems like anything else, but the difference is like trying to run Cubase through a Creative SB16.
For me Pro Tools was too expensive. I opted for using a Creamware system (about half the price). Same idea of using dedicated hardware with a PC environment acting as a fully configurable Studio. However it is designed to work with standard sequencer programs. I use Sonar, but it works just as well with Cubase. It basically lifts a lot of the processing weight of the system main CPU, running audio processing and generation algorithms on dedicated high performance DSPs.
Other companieas are begining to offer there kind of solutions. They're not cheap, but then neither is the sound.
Earlier on I was kidding about Cubase. There's not much between Cubase and Sonar. They've got slightly different emphasis in their tools and envoronment. My preference is simply for more flexibility and a preference in the way data is presented. With Modern day processing power on a PC you have to go a fair amount before you encounter the problems of bandwidth. Then again I have a Creamware system. so maybe I just don't get the problem.
Cheers
John